Electric energy storage devices with higher energy density and higher power density are required for hybrid electric vehicle use. We have investigated the structure and property of polyacenic semiconductor materials (PAS) and polycyclic aromatic hydrocarbons (PAHs) materials and the power characteristics (the resistance and the rate capability) of devices using the PAS or PAHs materials as negative electrodes. We focused on the effect of the particle size and the Li predoping amount on the power characteristics. We found that submicrometer particles of polyacenic semiconductor materials (PAS) with the Li predoping over 600 mAh/g have an excellent rate capability with current density over 500C. (c) 2007 The Electrochemical Society.